Field of the Invention
The present invention relates to a coil component and, more particularly, to a coil component that can be used as a coupling inductor. The present invention further relates to a circuit board in which such a coil component is embedded.
Description of Related Art
A coil component called “coupling inductor” may be used as a smoothing coil for a switching power supply such as a DC/DC converter. As described in Japanese Patent Application Laid-open Nos. 2013-526787 and 2015-130472, the coupling inductor has a configuration in which windings wound in opposite directions are magnetically coupled to each other. When a current is made to flow in one winding, an electromotive force is generated to make the current flow also in the other winding. Thus, when the coupling inductor is used as a switching power supply smoothing coil, an inrush current peak can be reduced.
A coil component described in Japanese Patent Application Laid-open No. 2013-526787 has a configuration in which a winding is made up of wire or foil. In FIG. 32 of Japanese Patent Application Laid-open No. 2013-526787, a configuration in which the end portions of two windings are connected to a common external terminal is illustrated. Further, Japanese Patent Application Laid-open No. 2015-130472 discloses a coil component obtained by forming a planar spiral conductor on both the front and back surfaces of an insulating substrate.
However, in the coil component described in Japanese Patent Application Laid-open No. 2013-526787, the winding is formed by a wire or a foil, which may complicate a manufacturing process and cause a large variation in characteristics obtained.
On the other hand, in the coil component described in Japanese Patent Application Laid-open No. 2015-130472, a spiral conductor is used as a winding, so that a variation in characteristics is small. However, in the invention of Japanese Patent Application Laid-open No. 2015-130472, two planar spiral conductors are wound concentrically, which may make adjustment of the magnetic coupling coefficient difficult. That is, in the coupling inductor, a leakage flux component free from magnetic coupling brings the smoothing action, so that in order to obtain desired characteristics, it is necessary to reduce the magnetic coupling coefficient to some extent and thus to ensure a sufficient leakage flux component. However, in order to reduce the magnetic coupling coefficient in the coil component described in Japanese Patent Application Laid-open No. JP 2015-130472, it is necessary to increase the interval between the two concentrically-wound planar spiral conductors. This may result in increase in the planar size of a product.